How can I independently pose Group Instances?
On Linux (have not tested on Mac) I recently used the following method to create layout for a shot that required 3 instances of a procedural rock creation rig. Then i created a proxy of the armature from each of the group instances and posed them accordingly.



Starting with two folders: one containing an asset file and the other where my shot file exists. In the asset file the Rig/Geometry is grouped.

blend:~/demoProceduralRocks&gt;&gt; ls
asset/ shot1/


Since I want to create create a scene that should have 3 identical instances of the asset, I create hard links to the file in the shot's import folder

blend:~/demoProceduralRocks&gt;&gt; cd shot1/import/

blend:~/demoProceduralRocks/shot1/import&gt;&gt; ln -v ../../asset/Rock.blend Rock.instance.1.blend

blend:~/demoProceduralRocks/shot1/import&gt;&gt; ln -v ../../asset/Rock.blend Rock.instance.2.blend

blend:~/demoProceduralRocks/shot1/import&gt;&gt; ln -v ../../asset/Rock.blend Rock.instance.3.blend


This is how it looks after creating hard links

blend:~/demoProceduralRocks&gt; ls -lirt asset/ shot1/import/
asset/:
total 172
22217836 -rw-rw-r-- 4 blend home 169297 2013-05-27 15:22 Rock.blend

shot1/import/:
total 516
22217836 -rw-rw-r-- 4 blend home 169297 2013-05-27 15:22 Rock.instance.3.blend
22217836 -rw-rw-r-- 4 blend home 169297 2013-05-27 15:22 Rock.instance.2.blend
22217836 -rw-rw-r-- 4 blend home 169297 2013-05-27 15:22 Rock.instance.1.blend 


Then I layout the shot file by linking the groups from the hard linked files created above. Then I make a proxy of the Armature and Pose each proxy separately. (A demo of this in action)

blend:~/demoProceduralRocks&gt; tree ./
./
|-- asset
|   `-- Rock.blend
`-- shot1
    |-- Layout.shot1.blend
    `-- import
        |-- Rock.instance.1.blend
        |-- Rock.instance.2.blend
        `-- Rock.instance.3.blend